The present invention relates to an igniter having a consumable flash tube for encapsulating igniter material and more particularly to an igniter having a flash tube for encapsulating igniter material for the propellant beds in propelling charges or rocket motors which functions as an environmental housing and additionally functions as a grounded electrical conductor or Faraday shield to bleed off any inadvertent electrical charge presented to the flash tube.
Prior art flash tubes or ignition devices for igniting propellant beds commonly consisted of a high strength, seamless, perforated steel tube for encapsulating the igniter material. The use of a steel tube was required to provide pressure confinement for the selected igniter material, black powder, and thereby increase burning rate so as to obtain the pressure buildup required for ignition. The steel tube is normally embedded in the propellant bed to be ignited. The steel tubes are expensive in material cost and require accurate and time consuming machining to tolerance. In addition, the steel tubes require special quality assurance inspection techniques to detect imperfections which could cause tube rupture during ignition and result in improper performance of the ignition assembly and propellant bed. These disadvantages can be overcome by encapsulating a fast burning igniter material, which does not require pressure confinement, in a consumable flash tube which is inexpensive and does not require elaborate and time consuming machining or inspection techniques. A fast burning igniter material does not require pressure confinement and thus allows a consumable flash tube to be used in the igniter.
Prior art consumable flash tubes are best typified by the devices disclosed in U.S. Pat. Nos. 3,645,206, to Quinlan et al, 3,696,749, to Scanlon, and 3,828,676, to Junker. The device of Quinlan et al discloses a consumable ignition system which ignites a molded charge of single based propellant encompassing a projectile. Quinlan et al fails to disclose either a consumable flash tube embedded in a propellant bed, per se, or a flash tube functioning as an electrical conductor or Faraday shield.
The device of Scanlon discloses an expendable cartridge provided with a consumable flash tube containing a booster propellant charge of black powder that is used to ignite the main charge. Scanlon does not disclose a flash tube which functions as an electrical conductor or Faraday shield so as to bleed off inadvertent electrical charge presented to the flash tube and thus limit the charge transferred to the igniter material.
The disclosure of Junker teaches a consumable explosive cartridge having a primer encased in a flexible nitrocellulose capsule. The capsule has a greater volume than the primer so as to facilitate safe handling of the primer during assembly. The larger volume of the capsule ensures that no pressure will be exerted on the primer during the assembly process and thus the cartridge is stable in regard to inadvertent physical shock but is subject to detonation when compressed in an appropriate firing chamber. Again, the device of Junker fails to disclose a flash tube provided with electrical charge dissipating material which functions as a grounded electrical conductor or Faraday shield to bleed off any inadvertent electrical charge presented to the flash tube and thus limit the charge transferred to the igniter.